This invention relates to an apparatus for conveying granular plastic material. Apparatuses of this kind are known and described, for example, in the publication VKD 415 from Filterwerk Mann and Hummel GmbH. These apparatuses serve to convey granular plastic materials of various compositions from silos to injection-molding machines. For this purpose, it is necessary to execute different processing steps, as, for instance, mixing various components and/or adding color pigments, proportioning and weighing the individual components, drying the granular plastic materials in appropriate drying devices and distributing the material flows to different processing systems.
Conveying devices such as, for example, those described in the publication VKD 439 from Mann and Hummel ProTec GmbH of MANN+HUMMEL ProTec GmbH have proven to be useful, particularly for conveying granular plastic materials. Such conveying devices serve to automatically charge tanks, balances, mixing and proportioning devices, as well as processing systems. They usually comprise a conveyor station and a blower station. With the known types of apparatuses for conveying granular plastic materials, it has been possible to process many types of plastic materials. Practice has shown, however, that types of granular materials which exhibit a high cohesiveness, such as, for example, silicone granules, tend to cake or to form lumps within the conventional conveying devices, thereby causing complications during the conveying process. Especially silicone in the form of blocks, strands or ribbons has been fed to the extruders of injection-molding machines by means of suitable feeding devices or stuffing devices. This process requires very complicated feeding devices and does not enable any proportioning or mixing of various components.
It is therefore the object of this invention to provide an apparatus for conveying granular plastic materials which enables processing and distribution of granular materials that in the past have been difficult to convey.
These and other objects have been achieved in accordance with the present invention by providing an apparatus for conveying a granular plastic material comprising a storage tank, a device for loosening granular plastic material disposed within the storage tank, and a discharge device for transporting the granular material to an extruder antechamber.
The substantial advantage of the present invention is that the storage tank provided for the granular plastic material comprises a device for loosening the plastic granules as well as a discharging device directly or indirectly feeding the granular material to an extruder antechamber. The device for loosening the granular plastic material may be, for example, a stirring arm or a stirring plate with blades arranged thereon, for gently keeping the granular material in motion. Another function of the stirring arm or stirring plate is to pre-proportion the material and then to feed it to the discharging device. In this case it is likewise necessary that the material be treated carefully.
It is also possible to use other mechanical devices or fluidizing devices which keep the granular material near the material discharging region in motion.
In accordance with another embodiment of the invention, the discharging device comprises a suction device in which the suction line is not supposed to extend in rising direction, so that it is assured that the granular material to be conveyed does not tend to form lumps.
Another embodiment of the invention is to arrange the device for sucking up material from the storage tank at a position where the granular plastic material is being loosened. It is furthermore advantageous to supply the fresh air portion required for operation of the suction device to the storage tank directly in this region, and to adjust the air supply continuously by means of suitable shutters or the like.
In accordance with a further embodiment of the present invention, a so-called granulate retaining element is provided at the suction outlet, so that it is not possible to take too much granular material from the storage tank via the suction device. This granulate retaining element is likewise adjustable and can be adapted to the material flow which is to be conveyed.
As can be seen, for example, from the aforementioned publication VKD 439, the conveying and suction process are carried out by means of conventional conveying devices. The conveying devices are advantageous because they have a compact structure and a separate blowing station, and the conveying process can be regulated variably.
Another embodiment of the invention is to arrange an intermediate hopper downstream of the conveying device. This intermediate hopper consists essentially of a slim, vertical pipe, i.e., a pipe having a relatively small diameter compared to its length. The advantage of this structure is that it is thus possible to reliably prevent the granular plastic materials from forming lumps or from agglomerating.
In another preferred embodiment of the invention, the intermediate hopper, i.e., that the pipe, comprises two parts. The upper part of the pipe is arranged rigidly, which means it is fixed rigidly to the mounting. The lower part is connected to a vibratory feeder. The vibratory feeder serves to proportion the granular plastic material into the extruder antechamber. The rigid connection between the vibratory feeder and the lower part of the intermediate hopper enables reliable transport of the granular plastic material from the intermediate hopper into the vibratory feeder. The upper and lower parts of the intermediate hopper are interconnected by means of a flexible collar.
In order to monitor, control and/or regulate the apparatus in an advantageous manner, sensors for detecting the filling level are arranged on various vessels. The sensor signals can be supplied to an electronic control device, whereupon the control device will adjust the system to the respective granular material required for the injection-molding machine and will likewise recognize any disruptions in the operation of the system.
These and other features of the preferred further embodiments of the invention are set out not only in the claims, but also in the description and in the drawings, it being possible for the individual features to be realized individually or jointly in the form of subcombinations in embodiments of the invention and also in other fields, and constituting independently patentable embodiments for which protection is hereby claimed.